This invention relates to an optical printer head including a light source constituted of a plurality of luminous dots, a light-amount correction method for correcting a light amount of luminous dots in the optical printer head so as to render the light amount uniform, and an optical printer for emitting light therefrom toward a record medium to form an image thereon.
The assignee proposed an optical printer wherein a fluorescent luminous tube acting as a luminous device is used as a light source for an optical printer head to form an image on a record medium such as, for example, a silver salt convenience film or the like.
The optical printer head constituted by the fluorescent luminous tube in the proposed optical printer includes an envelope of which an interior is evacuated at a high vacuum. The envelope is formed by assembling insulating substrates made of a glass plate or the like into a box-like structure. An anode substrate which constitutes a part of the envelope is formed on an inner surface thereof with anodes on each of which a phosphor layer emitting light due to impingement of electrons thereon is deposited. The anodes and phosphor layers, as shown in FIG. 6, cooperate with each other to constitute two luminous dot trains 108 and 109, which are formed by arranging a plurality of luminous dots 107 in two rows and in an offset manner in a main scanning direction. Also, the anode substrate is provided on the inner surface thereof with a plane control electrode, which is arranged so as to surround the luminous dots 107 and anode wirings. The envelope has filamentary cathodes stretchedly arranged therein so as to be positioned above the luminous dot trains 108 and 109 and extend along the luminous dot trains or in the main scanning direction. The filamentary cathodes each include a core wire made of tungsten or the like and an electron emitting material deposited on the core wire.
Feeding of electricity to each of the cathodes permits the core wire to generate heat, resulting in electrons being emitted from the electron emitting material. The electrons thus emitted are permitted to impinge on the phosphors of the anodes to which a drive voltage is selectively applied, resulting in the luminous dots selectively emitting light. The plane control electrode has a positive voltage constantly applied thereto during driving of the optical printer head, to thereby render an electric field in its neighboring region uniform.
In the optical printer thus constructed, a record medium and the optical printer head are moved relative to each other in a sub-scanning direction perpendicular to the main scanning direction of the luminous dot trains 108 and 109 during recording operation. Also, data on an image to be formed are fed to the optical printer head, to thereby permit the luminous dots 107 to emit light at predetermined timings in synchronism with relative movement between the record medium and the optical printer head. Such driving permits light of the luminous dots 107 of the optical printer head to be successively irradiated in a line parallel to the main scanning direction on the record medium for exposure thereof, leading to formation of the image on the record medium.
The luminous dots 107 of the optical printer head are varied in light amount or luminous intensity as indicated in FIG. 7(a) wherein a light amount of each of the luminous dots is found by measuring light amounts of all luminous dots 107. Also, the record medium on which recording operation is carried out by the optical printer head is generally constructed so as to carry out color development depending on a level of energy of light applied thereto or intensity of the light. Such construction of the record medium, when a light amount is varied among the luminous dots, causes a degree of color development of the record medium such as, for example, a density of a color developed on the record medium or the like to be varied at every portion of the record medium on which light is irradiated from each of the luminous dots.
In order to eliminate a variation in color development occurring on the record medium due to a variation in light amount among the luminous dots 107, it is carried out to measure a light amount of each of all luminous dots 107 obtained when the luminous dots are driven for luminescence under the same conditions. Then, a value required to keep a level of luminescence of each of the luminous dots uniform or constant is calculated from the light amount of each of the luminous dots 107 and then stored in the form of information for correction in a ROM or the like. The value may be, for example, information for controlling lighting time of each of the luminous dots. When the luminous dots are used for an optical printer, the thus-stored correction information of each of the luminous dots is used for control which permits the light amounts of all luminous dots 107 to be kept constant or uniform. The control may be, for example, control of lighting time of the luminous dots. More specifically, as shown in FIG. 7B, a level of the light amount of each of the luminous dots is adjusted so that the light amount of each of the luminous dots is aligned with that of the luminous dot 107 having a minimum light amount, resulting in ensuring that an image at a uniform density is obtained on the record medium.
However, the fluorescent luminous tube acting as a light source for the optical printer head is so constructed that the filamentary cathodes each are welded at both end thereof to a stretch fitment, to thereby be stretchedly arranged in the envelope. Such construction causes a part of heat generated by the core wire of each of the filamentary cathodes to be absorbed by the stretch fitment. This fails to increase a temperature of the cathode to a level sufficient to permit the cathode to emit electrons, leading to an end cool phenomenon which causes both ends of the cathode to fail to emit a sufficient amount of electrons as compared with a central portion thereof. More specifically, this causes a substantial difference in light amount between the luminous dots 107 positioned at both ends of the cathodes and those positioned at other regions thereof, so that the luminous dots 107 at both ends are decreased in light amount as compared with those at the other regions.
Light-amount correction of the luminous dots 107 which is carried out in the prior art in order to eliminate such a difference in light amount causes light amounts of all luminous dots 107 to be corrected so as to be at a level of light amounts of the luminous dots positioned at both ends of the fluorescent luminous tube defined in the main scanning direction.
Also, in the record medium exposed to light emitted from the optical printer head, the luminous dots 107 arranged at both ends of the fluorescent luminous tube in the main scanning direction, as shown in FIG. 6, are positioned out of an effective printing range H or allocated to an ineffective printing range h which permits a variation in light amount of the luminous dots 107 to be substantially disregarded.
Thus, light-amount correction of the luminous dots 107 causes all luminous dots 107 to be set at a light-amount level equal to that of the luminous dots 107 which are out of the effective printing range H or in the ineffective printing range h which permits a variation in light amount of the luminous dots 107 to be substantially disregarded. This leads to a reduction in light amount of the luminous dots 107 in the effective printing range H which contributes to recording on the record medium, so that the luminous dot trains 108 and 109 fail to feed exposure energy at a sufficient level to the record medium without adversely affecting quality of an image to be formed, resulting in loss of the exposure energy.
The present invention has been made in view of the foregoing disadvantage of the prior art.
Accordingly, it is an object of the present invention to provide an optical printer head which is capable of increasing a level of a light amount for exposure emitted from luminous dot trains in view of an end cool phenomenon caused by filamentary cathodes.
It is another object of the present invention to provide an optical printer head which is capable of reducing loss of exposure energy.
It is a further object of the present invention to provide a light-amount correction method for an optical printer head which is capable of correcting a light amount of luminous dots in view of an end cool phenomenon caused by filamentary cathodes.
It is still another object of the present invention to provide an optical printer which is capable of ensuring formation of an image increased in quality on a record medium in view of an end cold phenomenon caused by filamentary cathodes.
In accordance with one aspect of the present invention, an optical printer head is provided. The optical printer head includes a light source constituted by luminous dot trains each including a plurality of luminous dots and a memory device for storing therein correction information obtained by light-amount correction carried out for ensuring uniform luminescence of the luminous dots. The light-amount correction is carried out on the luminous dots in an effective printing range of the luminous dot trains other than the luminous dots in an ineffective printing range of the luminous dot trains while omitting the luminous dots in the ineffective printing range from the light-amount correction, so that correction information obtained by the light-amount correction carried out on the luminous dots in the effective printing range is stored in said memory device. In the optical printer head of the present invention, the luminous dots of each of the luminous dot trains of the light source each include an anode arranged on an anode substrate and a phosphor layer deposited on the anode. The light source also includes filamentary cathodes arranged above the luminous dot trains so as to extend along the luminous dot trains. In the optical printer head of the present invention, the ineffective printing range includes luminous dots positioned in proximity to each of both ends of the luminous dot trains. The luminous dots in the ineffective printing range each may exhibit a light amount of about 80% or less based on an average light amount of the luminous dot trains. The luminous dots in the ineffective printing range may be constantly kept excited for luminescence, wherein a record medium which is rendered white due to exposure thereof to light of the luminous dots may be used, resulting in a white frame being formed on each of both ends of the record medium. The correction information may be based on a minimum value of a light amount of the luminous dots in the effective printing range.
In accordance with another aspect of the present invention, a light-amount correction method for an optical printer head is provided. The light-amount correction method includes the steps of measuring luminescent output of each of luminous dot trains constituted by a plurality of luminous dots and carrying out light-amount correction for rendering a light-amount of each of the luminous dots uniform depending on the luminescent output measured, to thereby previously obtain correction information, resulting in carrying out the light-amount correction of the luminous dots depending on the correction information. The light-amount correction is carried out on the luminous dots in an effective printing range of the luminous dot trains other than the luminous dots in an ineffective printing range of the luminous dot trains while omitting the luminous dots in the ineffective printing range from the light-amount correction, so that correction information obtained by the light-amount correction carried out on the luminous dots in the effective printing range is stored in the memory device, leading to the light-amount correction of the luminous dots in the effective printing range. In the method of the present invention, the ineffective printing range includes luminous dots positioned in proximity to each of both ends of the luminous dot trains. The correction information is based on a minimum value of a light amount of the luminous dots in the effective printing range.
In accordance with a further aspect of the present invention, an optical printer is provided. The optical printer includes a light source including luminous dot trains each constituted by a plurality of luminous dots, a record medium irradiated thereon with light from the light source, resulting in an image being formed thereon, a transfer means for moving the light source and record medium relative to each other, a control means for driving the transfer means and light source in synchronism with each other, and a memory device for storing therein correction information obtained by light-amount correction carried out for ensuring uniform luminescence of the luminous dots. The light-amount correction is carried out on the luminous dots in an effective printing range of the luminous dot trains other than the luminous dots in an ineffective printing range of the luminous dot trains while omitting the luminous dots in the ineffective printing range from the light-amount correction, so that correction information obtained by the light-amount correction carried out on the luminous dots in the effective printing range is stored in the memory device, leading to driving of the light source depending on the correction information. In the optical printer of the present invention, the luminous dots of each of the luminous dot trains of the light source each include an anode arranged on an anode substrate and a phosphor layer deposited on the anode. The light source also includes filamentary cathodes arranged above the luminous dot trains so as to extend along the luminous dot trains. In the optical printer of the present invention, the ineffective printing range includes luminous dots positioned in proximity to each of both ends of the luminous dot trains. The correction information may be based on a minimum value of a light amount of the luminous dots in the effective printing range.